1. Field of the Invention
The present invention relates to a pel (i.e.,picture element,or pixel) drive circuit for selectively driving pels arranged in a matrix configuration, to a combination pel-drive-circuit/pel-integrated device comprising the pel drive circuit, and to a liquid display device incorporating the combination pel-drive-circuit/pel-integrated device.
2. Description of the Related Art
Recently, liquid crystal display devices have come into use as image display devices matching the performance of cathode-ray tubes (CRTs). The liquid crystal display device comprises pels arranged in the horizontal and vertical directions so as to form a matrix, and shift registers disposed in each of the horizontal and vertical directions. A vertical selection pulse signal is output from the vertical shift register while being sequentially shifted in the vertical direction. Every time a pel line (a row of pels aligned in the horizontal direction) is selected, a horizontal shift register outputs a horizontal selection pulse signal while being sequentially shifted in the horizontal direction. Pels of the pel line selected by the vertical selection pulse are scanned and sequentially selected. Through repetition of the foregoing operations, video signals are written into all the pels.
In the field of image display devices of this type, there is also known a multi-scan-compatible display device whose display area can be changed according to the type of a video signal in order to be able to cope with video signals complying with various standards, in the same way as does an image display device using a CRT. Under the method employed by the image display device of such a type, a non-display area (e.g., top and bottom margins of the screen) of the screen is made dark by not supplying the vertical selection pulse, thereby adjusting the size of a display area. This method eliminates a necessity for modifying the video signal itself, yielding the advantage of eliminating necessity for a control circuit or image memory for processing a video signal, as well as reducing the degree of increase in cost.
In the conventional image display device set forth, transfer stages in the vertical shift register are provided so as to correspond to the respective vertical pel lines. Pulses are shifted and output in the vertical direction one by one. The recent tendency for pursuit of a further reduction in pel pitch in association with a demand for a display image of higher definition complicates an attempt to form one transfer stage of the shift register within an area equal to that occupied by one pel line, which has conventionally been feasible. Even if such a high-density layout of transfer stages of the shift register becomes possible as a result of improvement in the technology for miniaturizing a semiconductor element, in a case where transfer stages of the shift register are provided for respective pel lines, the total number of semiconductor elements, such as transistors, required for constituting the entire shift register cannot be diminished, and hence the amount of electric current consumed by the shift register cannot be reduced. Further, in a case where a pulse is transferred in the shift register on a per-pel-line-basis, as in the case with the conventional image display device, an attempt to increase the number of pel lines involves a necessity for increasing the rate at which a pulse is transferred among transfer stages in the shift register. For this reason, the operating speed of semiconductor elements constituting a circuit of each transfer stage or a circuit of other portions must be increased; i.e., a drive frequency used for activating the semiconductor elements must be increased to a greater extent.
In the previously-described conventional multi-scan display device, an open-close switching element is provided for each of pel lines in the non-display area of the entire screen in order to interrupt the supply of a selection pulse to these pel lines. As a result, the number of elements used for each transfer stage is increased, which in turn increases the amount of electric current dissipated by the overall drive circuit. Particularly, under the current situation in which a further reduction in pel pitch is desired, provision of a switching element for each pel line is almost impossible, because forming a circuit for one transfer stage of the shift register within an area equal to that occupied by one pel line is nearly impossible.
As mentioned above, the conventional image display device encounters a problem in further reducing pel pitch and increasing the number of pels and suffers a necessity for increasing operating speed of elements constituting a drive circuit,
The present invention has been conceived in view of the foregoing problems, and the object of the present invention is to provide a pel drive circuit, a combination pel-drive-circuit/pel-integrated device, and a liquid display device incorporating the combination pel-drive-circuit/pel-integrated device, which readily enable a reduction in pel pitch and an increase in the number of pels without involvement of a necessity for increasing operating speed and the number of constituent elements for drive purposes.
According to a first aspect of the present invention, there is provided a pel drive circuit for driving a plurality of pels arranged in two different directions, comprising: pulse shift means which sequentially outputs a first pulse signal while shifting the first pulse signal in one of the two directions in units comprising a plurality of pels; and individual drive pulse generation means which generates, on the basis of the first pulse signal output from the pulse shift means, a larger number of second pulse signals for individually driving pel lines arranged in the other of the two directions. Here, the pel drive circuit may further comprise changeover means which is provided between the pulse drive means and the individual drive pulse generation means and which can selectively effect supply of the first pulse signal received from the pulse shift means, to the individual drive pulse generation means.
According to another aspect of the present invention, there is provided a combination pel-drive-circuit/pel-integrated device, comprising: a plurality of pels arranged in two different directions; pulse shift means for sequentially outputting a first pulse signal while shifting the first pulse signal in one of the two directions in units comprising a plurality of pels; and individual drive pulse generation means which generates, on the basis of the first pulse signal output from the pulse shift means, a larger number of second pulse signals for individually driving pel lines arranged in the other of the two directions. The combination pel-drive-circuit/pel-integrated device may further comprise changeover means which is provided between the pulse drive means and the individual drive pulse generation means and which can selectively effect supply of the first pulse signal received from the pulse shift means, to the individual drive pulse generation means.
According to still another aspect of the present invention, there is provided a liquid crystal display device comprising: a first substrate on which a plurality of pels are arranged in two different directions and on which a drive circuit is formed around the plurality of pels, a second substrate placed so as to oppose and be spaced a given interval away from the first substrate; and a liquid crystal layer held between the first and second substrates, wherein the drive circuit comprises: pulse shift means for sequentially outputting a first pulse signal while shifting the first pulse signal in one of the two directions in units comprising a plurality of pels; and individual drive pulse generation means which generates, on the basis of the first pulse signal output from the pulse shift means, a larger number of second pulse signals for individually driving pel lines arranged in the other of the two directions.
The liquid crystal display device may further comprise changeover means which is provided between the pulse drive means and the individual drive pulse generation means and which can selectively effect supply of the first pulse signal from the pulse shift means, to the individual drive pulse generation means.
In the pel drive circuit, the combination pel-drive-circuit/pel-integrated device, and the liquid crystal display device according to the present invention, the pulse shift means sequentially outputs a first pulse signal while shifting the first pulse signal in one of the two directions in units comprising a plurality of pels. The individual drive pulse generation means generates, on the basis of the first pulse signal output from the pulse shift means, second pulse signals for individually driving pel lines arranged in the other of the two directions. Further, changeover means is provided between the pulse drive means and the individual drive pulse generation means and can selectively supply the first pulse signal from the pulse shift means, to the individual drive pulse generation means. As a result, the range of effective pel lines of the pel lines arranged in the other direction, i.e., an active display area, can be switched.
Other and further objects, features, and advantages of the present invention will become more apparent from the following description.